Engineering & Mining Journal

MAY 2019

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68 E&MJ • MAY 2019 www.e-mj.com OPERATING STRATEGIES Moving pumpable but diffi cult-to-han- dle, semiliquid materials such as paste, slurry and sludge can be an expensive, troublesome job — particularly when using equipment that's not designed for reliability and fl exibility. Here are a few examples of products made to meet the tough demands of the task. Paste Backfi ll-diverter Valve Choice Pays Off for Nickel Mine Maintaining safe continuous operations is critical to mine profi tability. In the case of nickel mines, which have had to contend with price volatility for the last few years, it is even more important to be up and running now that prices seem to have stabilized. The Flying Fox mine in Western Aus- tralia is one of the highest-grade nickel mines in the world. Production from the mine, which reaches a depth of more than 1 kilometer (km) began, in 2006. Compa- ny statistics compiled since the opening of the mine show that it consistently has met or exceeded production targets, while maintaining the lowest production cost of any mine in Australia. According to Paul Seale, Forrestania Nickel Project paste fi ll foreman, main- taining high production levels is a top priority, and decisions regarding improve- ments and expansions are predicated on fi nding the best and most reliable compo- nents and equipment. Seale explained that in sourcing a di- verter valve for Flying Fox's 5,000-kPa (725-psi) paste backfi ll system, he was looking for a valve specifi cally designed for use in paste backfi ll mining opera- tions because of the demands placed on the valve. Seale ultimately selected a Victaulic 6-in. Series 725 two-port divert- er valve for use in the paste reticulation process. The coupling end connections allowed for fast changeouts of attached piping as the piping wears, along with simple maintenance access when nec- essary. While the valve is available with a variety of actuation options, Flying Fox chose an electrically actuated version. The valve was tied into the mine's pro- grammable logic controller (PLC) system, allowing for both local and remote oper- ation, which limits operator exposure to potential hazards. "This unit was selected based on its compatibility with the system and the fact that we could use it to isolate be- tween the separate underground reticula- tion lines or possibly as a dump valve in an emergency," Seale said. At the time of purchase, the owner as- sumed the valve would be sacrifi ced if cir- cumstances led its use as a dump valve. With that eventuality in mind, Seale said, a second valve was acquired at the same time so there would be a spare on site. As installed, the valve sits at the base of a 625-m (2,050-ft) vertical borehole that is cased with 89.9-mm (3.54-in.) internal diameter P110 drill casing. "We wanted a robust valve at the base of this borehole as insurance against pipe block- age," Seale said. According to Seale, the valve was in- dexed from one stope to another three or four times per week with reliable results. "We were able to fl ush the valve from sur- face using the head pressure of 625 m (2,050 ft) and air connected at surface," he explained. "Essentially, we have had trouble-free operation out of the valve." Valve performance was so exceptional that other mining companies visited the site to examine the system and diverter valve more closely. In addition to preventing blockages during normal operations, the diverter valve also has served as a dump valve in emergency scenarios to relieve potential blockages and pressure spikes. Seale not- ed that Flying Fox had "been saved on a number of occasions by being able to release paste from the borehole." In the 18 to 24 months following in- stallation, circumstances at the site led to fi ve or six emergency instances in which the valve had to be actuated under 6,000 to 7,000 kPa (870 to 1,015 psi) and safe- ly released under this load. According to Seale, using the valve this way prevented considerable downtime, and if the valve had not been actuated in these emergen- cies, the casing would have been lost. "In the absence of a way to evacu- ate the borehole, the paste would have seized and blocked the pipe, requiring the entire system to be replaced," he said. "If that had happened, we would have had to disconnect the plant from the borehole and bring in cranes and Cost-effective Equipment Choices for Paste, Sludge, Slurry Handling This Victaulic Series 725 two-port diverter valve saves the Flying Fox nickel mine an estimated A$1 million in repair and replacement costs in its paste backfi ll operations.

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